Tobacco-smoke filters

ABSTRACT

A tobacco-smoke filter comprises a tube of smoke-filtering sheet material, for example paper, extending longitudinally within and spaced radially from an outer tubular wrapper, for example an extruded smoke-impervious plastics material, the tube being blocked at both ends, while the space between the tube and the wrapper is blocked around complementary arcs at opposite ends and longitudinally in such manner that smoke entering at one end must pass through the wall of the tube twice before reaching the other end. Suitably the wrapper is formed or provided at intervals around its circumference with a number of longitudinal ribs for supporting the tube.

United States Patent 11 1 1111 3,830,244

Luke Aug. 20, 1974 TOBACCO-SMOKE FILTERS [75] Inventor: John A. Luke, Southampton, Primary Examiner-Robert Michell Assistant Examiner-John F. Pitrelli England Attorney, Agent, or Firm-Finnegan, Henderson, [73] Assignee: Brown & Williamson Tobacco Farab w & Garrett Corporation, Louisville, Ky. [22] Filed: Mar. 31, 1972 [57] ABSTRACT [21] Appl. No.: 240,174 A tobacco-smoke filter comprises a tube of smokefiltering sheet material, for example paper, extending Fmig" Application Primity Data longitudinally within and spaced radially from an April 16, 1971 Great Britain ..9632/71 outer tubular wrapper, for example an extruded smoke-impervious plastics material, the tube being [52]v US. Cl. 131/261 B, 131/210 blocked at both ends, while the space between the [51] Int. Cl. A24d 1/04, A24f 7/04, A24f 13/06 tube and the wrapper is blocked around complemen- [58] Field of Search 131/ 10.5, 10.7, 261 B, tary arcs at opposite ends and longitudinally in such 131/210 manner that smoke entering at one end must pass through the wall of the tube twice before reaching the [56] References Cited other end. Suitably the wrapper is formed or provided UNI AT PATENTS at intervals around its circumference with a number of 3,336,928 8/1967 Morehouse 131 105 longitudinal ribs for SuPPmting the tube- 3,359,988 12/1967 Thomson 131/261 B UX 5 Claims, 4 Drawing Figures 3,370,594 2/1968 Haslam l3l/l0.5 X

3,394,713 7/1968 Thomson et al l3l/l0.S X 3,502,087 3/1970 Romano l3l/10.5 X

TOBACCO-SMOKE FILTERS This invention concerns improvements relating to cigarette and other tobacco-smoke filters.

A filter in accordance with the invention comprises a smoke-porous tube of smoke-filtering sheet material extending substantially longitudinally within and spaced radially from an outer tubular wrapper, the tube being blocked at both ends, and the space between the tube and the wrapper being blocked around complementary arcs at opposite ends and longitudinally in such manner that smoke entering that space at one end is forced to pass through the wall of the tube twice before reaching the other, outlet, end.

For example, in the case of a cigarette filter, the wrapper may be made of an extruded smokeimpervious plastics material and may be formed or provided at intervals around its circumference with a number of longitudinal, internal, ribs for supporting the tube, generally concentrically, along its length. The tube may be made of porous filter paper.

Smoke-impervious plugs, for example of plastics material, may be used for blocking the tube 4 at its two ends. The annular space between the wrapper and the wall of the tube may closed by similar material at each end, the closures being offset or displaced by 180 one from the other. On smoking a cigarette through a filter of this construction, the smoke will enter through the half-annular opening at one end and pass through the tube wall to the inside of the tube, whence it will be constrained to pass through the said wall on the opposite side and out through the half-annular opening at the other end. Thesmoke is prevented from passing circumferentially around the tube by the longitudinal ribs, which block this path, but can pass through the wall of the tube along its whole length.

One embodiment of the invention will now be more fully described with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section, on the lines l-I in FIG. 2, through a cigarette filter,

FIG. 2 an end view thereof,

FIG. 3 a diagrammatic side view of a form of apparatus which can be used in the production of such filters, and

FIG. 4 a plan view of a part of the said apparatus.

The single filter illustrated to an enlarged scale in F IGS. l and 2 comprises a tube 1 of smoke-filter paper located co-axially within a tubular wrapper or casing 2 made of a substantially smoke-impermeable plastics or other softenable material, such as polyethylene, polypropylene, ethylene vinyl acetate copolymer, polyvinyl chloride, polystyrene, cellulose acetate or the like. Suitably, it is made of polyethylene. The tube 1 is located and supported in the wrapper 2 by longitudinal internal ribs 3 formed integrally with the latter at intervals around its circumference. At each end of the filter, the interior 4 of the tube 1 is closed by a short cylindri cal or disc-shaped plug 5 of substantially smokeimpermeable plastics material such as extruded, solid or foamed, polyethylene, polypropylene, ethylene vinyl-acetate copolymer, nylon, polyurethane or cellulose acetate, for instance a white cellulose acetate rendered impermeable by the use of a high concentration of plasticizer. Suitably it is made of polyethylene.

By reason of the ribs 3, there is a narrow annular space 6 between the tube 1 and the wrapper 2. This space is closed around half of the circumference of the filter at one end thereof and around the other half of the circumference at the other end. Closure is effected by an intumed lip on the wrapper 2. In FIG. 2, which is a view of the left-hand end in FIG. 1, such a lip 7a is shown extending around one half of the circumference between ribs 3a and 3b. At the other end, a similar lip 7b, offset angularly by extends around the other half of the circumference between the said ribs 3a and 3b, as indicated by the are marked 7b in FIG. 2. The lips 7a, 7b may be produced and sealed to the tube 1 by the application of heat and pressure to the wrapper 2. However, the seal may be assisted by adhesive, for example a polyvinyl-acetate adhesive.

On smoking a cigarette through a filter such as is shown in FIGS. 1 and 2, the smoke will enter the open one half (circumferentially) of the annular space 6 at one end, say the right-hand end in FIG. 1, and pass through thewall of the filter tube 1 to the interior 4 thereof, whence it will then be constrained to pass through the said wall on the opposite side into the other half of the said space 6 and out through the open lefthand endof the latter. The smoke is prevented from passing circumferentially around the wall of the tube 1 by the ribs 3. In particular the ribs 3a and 3b prevent the smoke from passing directly from one half of the annular space 6 into the other. The smoke can, however, pass through the filter-tube wall along its whole length. As will be evident, all of the smoke is forced to pass twice through the filtering material of the tube 1. However, this double passage through filtering material is achieved with a compact filter and economic use of materials. Finally, the filter lends itself to reliable production at high speed and by simple apparatus.

One form of apparatus by which such filters can be produced will not be described by way of example. In this apparatus, filters are produced initially, as is commonly done, in lengths providing four such filters, which are subsequently cut into single filters.

Referring to FIG. 3, a strap 10 of filter paper for the tube 1 is supplied from a bobbin l1, plastics-rod material 12 for the plugs 5 from a reel 13, plastics material for the wrapper 2 from an extruder press 14 and, if required, paper strip 15 for a conventional outer filter wrapping from a bobbin 16. From the bobbin 11, the strip 10 is fed through an applicator 17 by which both edges are provided with heat-activatable adhesive for the eventual production of a longitudinal tube seam. The strip 10 then passes through a cooler 18, which renders the adhesive inactive, to a device 19 for cutting predetermined lengths 5a, equal to the length of two plugs 5, from the rod 12 and placing them on the strip l0 at predetermined intervals. For example, for the case of a filter 20 mm long, the lengths 5a may be 5 mm and the interval 20 mm.

The rod 12 arriving at the device 19 passes between a serrated feed roller 20 and a circumferentially grooved guide roller 22. It advances along a groove in a platform towards the end of which the lengths 5a are cut off by a rotary knife 26, of a type well known in the cigarette industry. Each severed length 5a is engaged by a transfer wheel 28 and is carried through a guide past an electrical heater so as to be deposited on the strip 10. The strip 10, carrying the plug-lengths 5a, advances between a circumferentially grooves roller 31 and a plain roller 33. The rollers 20, 22, knife 26, wheel 28 and rollers 31 and 33 are driven from a common drive shaft at co-ordinated speeds so as to produce the predetermined lengths 5a of plug material and to deposit them at the predetermined intervals on the strip 10. Separation of the lengths 5a is achieved by driving the wheel 28 with a higher peripheral speed than that of the rollers 20, 22. The heater serves to activate heatactivatable adhesive with which the rod 12 is precoated, so that the plug lengths 5a adhere to the strip where they are deposited.

The paper strip 10 carrying the lengths 5a of plug material progresses through a forming unit 34 in which it is brought to tube form around the said lengths and a heated sealing unit 35 by which the edges of the strip are sealed together and the plug lengths are sealed to the tube, followed by a cater-pillar traction unit 36. The units 34 to 36 may be of known kind such as are used for producing tubular paper wrappings in cigarette-making or filter-making machines. Advantageously, however, the units 34 and 35 are devised to form the tube with a butt joint rather'than a lap joint.

The assembly 10a thus produced and consisting of the strip 10 wrapped as a tube around the plug lengths 5a is next supplied by means of an extruder cross-head die 37 with a tubular wrapping of plastics material which provides the wrapper 2 of the eventual filters.

The extruded assembly 10b then passes with or without an outer wrapping strip 15, into a garniture 49. If a strip 15 is not wrapped around the assembly 10b, the garniture 49, which may be of the kind well known in the cigarette industry, serves mainly as a haul-off device by the action of the customary garniture tape. If an outer wrapping strip 15 is provided, the garniture serves also to form the strip around the assembly 10b and to consolidate the whole assembly. Housed with the garniture is a cut-off device, operative at 50, which divides the assembly 10b midway of every fourth plug length 5a. For the case of the above example of filters mm long, the assembly 10b is thus divided into 80 mm lengths 100, each comprising material for four single-filter lengths. Division into the single-filter lengths is effected at a later stage, for example in known manner during the assembly of filter tip cigarettes incorporating the filters.

The lengths 100 are supplied singly to a conveyor 51 by which they are advanced under an electrical heater 52 with projecting ribs 59 which press the material of the wrapper 2 into the paper tube 1 to produce the seals 7a and 7b of the inner single filters at intermediate points in each length 10c and past electricall1eaters 53 at each side with ribs 60 for similarly producing the seals at the ends of that said length. The conveyor 51 comprises a pair of endless chains each supporting a series of spaced recessed carried blocks which hold the lengths 10c, deposited transversely thereon, freely near the ends, but with some overhang. The lengths are carried along by the operative upper flight of the conveyor 51 in light contact with a fixed plate so that they are caused to roll in the recesses and, in passing the heaters 52 and 53 are formed with the aforesaid seals. The ribs 59,60 are dimensioned and positioned to produce half-circular seals 7a and 7b of the required length and locations circumferentially of the filters. The filterrod lengths 100 are finally discharged from the conveyor 51 at 62.

I claim 1. A tobacco-smoke filter comprising a smokeporous tube of smoke-filtering sheet material having a wall and extending substantially longitudinally within and spaced radially from an outer tubular wrapper, a block at each end of the tube and a smoke passage chamber therebetween, and an inturned lip extending from said wrapper at opposite ends thereof through subtending complementary arcs totalling 360, whereby the space between the tube and the wrapper is blocked around subtending complementary arcs at opposite ends and longitudinally from arc to are so that smoke entering the said space at one end is constrained to pass through the wall of the tube twice before reaching the other end.

2. A filter according to claim 1, wherein the wrapper has, at intervals around its circumference, a number of longitudinal internal ribs for supporting the tube along its length.

3. A filter according to claim 1, wherein the wrapper is made of an extruded smoke-impervious plastics material.

4. A filter according to claim 1, wherein said inturned lip comprises circumferential seals around semicircular arcs offset by 180 one from the other.

5. A filter according to claim 1, wherein said inturned lip comprises circumferential seals around semicircular arcs offset by 180 one from the other, the said seals extending circumferentially between the same longitudinal ribs, but around the said offset arcs, at the opposite ends of the filter. 

1. A tobacco-smoke filter comprising a smoke-porous tube of smoke-filtering sheet materiAl having a wall and extending substantially longitudinally within and spaced radially from an outer tubular wrapper, a block at each end of the tube and a smoke passage chamber therebetween, and an inturned lip extending from said wrapper at opposite ends thereof through subtending complementary arcs totalling 360*, whereby the space between the tube and the wrapper is blocked around subtending complementary arcs at opposite ends and longitudinally from arc to arc so that smoke entering the said space at one end is constrained to pass through the wall of the tube twice before reaching the other end.
 2. A filter according to claim 1, wherein the wrapper has, at intervals around its circumference, a number of longitudinal internal ribs for supporting the tube along its length.
 3. A filter according to claim 1, wherein the wrapper is made of an extruded smoke-impervious plastics material.
 4. A filter according to claim 1, wherein said inturned lip comprises circumferential seals around semi-circular arcs offset by 180* one from the other.
 5. A filter according to claim 1, wherein said inturned lip comprises circumferential seals around semi-circular arcs offset by 180* one from the other, the said seals extending circumferentially between the same longitudinal ribs, but around the said offset arcs, at the opposite ends of the filter. 